The invention has been devised primarily in the context of (but is not limited to) seals for centrifugal pumps. A typical centrifugal pump includes an impeller that rotates in a pump chamber to draw liquid into the chamber through a central inlet and direct the liquid radially outwardly by centrifugal force to an outlet at the periphery of the chamber. The impeller is mounted at one end of a rotary drive shaft that extends outwardly through a housing that defines the pump chamber. Externally of the chamber, the shaft is supported in bearings and is coupled to a suitable drive motor. A seal is provided where the shaft extends through the housing defining the pump chamber.
Conventionally, two alternative types of seal have been employed, namely a traditional so-called pump “packing” or a composite mechanical seal. A traditional pump packing includes a housing into which packing rings are inserted and then compressed by means of a packing gland so that the rings seat snugly against the shaft. A mechanical seal involves a complex assembly of seal components that co-operate with one another to provide the required sealing effect. This type of seal is quite expensive both in terms of capital cost and initial set-up time and complexity.
Seals deteriorate rapidly in pumps that are used in harsh environments such as for pumping acid in paper mills. The seals must be replaced at frequent intervals, and the pump must be shut down each time. This is costly not only in terms of direct maintenance cost, but also in terms of pump down time.